Parkinson's Disease (PD) is a movement disorder causing either uncontrolled movement, slowness of movement, slowness of initiation of movement or rigidity of muscles. Deep Brain Stimulation (DBS) is the FDA-approved method for patients who no longer get effective treatment from the best available medication. The location in the brain where the electrode is placed during DBS surgery for PD is called the Subthalamic Nucleus or STN. This study aims to investigate another location in the brain, the Substantia nigra pars reticulata or SNr. The SNr is also known to be involved in motor control of muscles and may be involved in the process by which the initiation of movement occurs.

Parkinson's Disease (PD) is a movement disorder causing either uncontrolled movement, slowness of movement, slowness of initiation of movement or rigidity of muscles. One method of easing PD symptoms is the FDA-approved method of Deep Brain Stimulation (DBS) for patients who no longer get effective treatment from the best available medication. The location in the brain where the electrode is placed during DBS surgery for PD is called the Subthalamic Nucleus or STN. During placement of the DBS electrode, the patient is awake and is asked to do motor tasks to determine the correct placement in the STN and proper functioning of the DBS electrode. This study aims to investigate another location in the brain, the Substantia nigra pars reticulata or SNr, during the normal placement of the DBS electrode. This location is also known to be involved in motor control of muscles and may be involved in the process by which the initiation of movement occurs. The path through the brain to the STN used for DBS surgery goes into the SNr but currently, no testing of the SNr is performed. We will conduct a simple and well documented visual motor test to document the patient's stimulus perception and motor intention both at rest and during neural stimulation of the SNr.

Inclusion Criteria:

• Clinical diagnosis of Parkinson's disease
• must be able to undergo awake surgery DBS
• must have unaided vision to view visual motor task

Exclusion Criteria:

• corrective eyeglasses or contact lenses

Patients with Parkinson's disease who are candidates for Deep Brain Stimulation surgery.